1. Field of Invention
The present invention relates to an electrical connection box which in use is mounted on a vehicle, such as an automobile, and is adapted to be connected to an electrical power source of the vehicle, particularly a high voltage power source. The invention further relates to a vehicle having such an electrical connection box mounted thereon.
2. Description of Related Art
Normally one secondary, i.e. rechargeable, battery having a rated voltage of 12V and a maximum nominal voltage of 14V is mounted on an automobile of the internal combustion engine type. A voltage up to the maximum voltage of 14V is applied from the battery to a circuit composed of bus bars and the like that are accommodated in an electrical connection box. The power supply is distributed by the internal circuit of the electrical connection box. The operation of electric/electronic component parts mounted on the vehicle is controlled through electric wires connected with the internal circuit.
On a goods vehicle, such as a lorry or truck, a rated voltage of 24V and a maximum voltage of 28V are applied to a circuit by a battery structure.
In recent years, electric/electronic component parts have been mounted in increasing numbers on a vehicle, and there is an increase in the electric current which is applied to one electric/electronic component part. For example, the electric power required to drive a fan is conventionally 130 watts, but has become 260 watts in recent years. At the rated voltage of 12V of the battery, it is impossible to operate suction and exhaust devices of an engine, electromotive power steering, and the like devices, requiring a high voltage such as 36V. Therefore, they are mechanically operated by the driving force of the engine.
With the increase of the electric current applied to each electric/electronic component part, the diameter of the electric wires used has become larger. Further, with rapid increase of the number of electric/electronic component parts, the number of electric wires has increased recently, which has increased the diameter of a wire harness having a bundle of electric wires. Consequently, the weight of the electric wires to be wired on a vehicle body has increased.
As described above, if the power supply from the battery is incapable of operating the suction and exhaust devices of the engine, they are mechanically operated. In this case, it is impossible to accomplish fine control of the operation of the suction and exhaust devices. Further, much fuel is consumed, which pollutes the environment. Accordingly, it is preferable to operate the suction and exhaust devices of the engine and the like not mechanically but electrically by the power supply from the battery.
In the case where the circuit is so constructed that a voltage higher than 14V can be applied to the circuit of the electrical connection box composed of bus bars and the like, it is possible to reduce the required electric current and thus the diameter of the electric wires and the size of a bundle of a plurality of electric wires (wire harness). Therefore, it is possible to reduce the weight of the electric wires.
Further, with the application of a high voltage to the circuit composed of bus bars and the like, it is possible to control the operation of the suction and exhaust devices, the power steering motor, and the like not mechanically or hydraulically but electrically. In this case, it is possible to accomplish fine control of the operation of suction and exhaust devices and the like. Further, fuel consumption can be reduced, which reduces pollution.
It is preferable to apply a high voltage of about 42V to the electromotive power steering motor, the suction and exhaust devices of the engine, the fan, and/or other devices requiring a high voltage. On the other hand, in an automobile, it is preferable to apply the rated voltage of 12V (maximum voltage: 14V) to signal-generating devices of the electric/electrical component parts and coils of relays.
In the case where the electrical connection box, with a circuit to which a high voltage of about 42V is applied, is mounted in the engine compartment of the vehicle, drops of water are liable to penetrate into the electrical connection box through gaps at a relay receiving element, a connector receiving element or a fuse receiving element, thus penetrating into gaps between high-voltage bus bars and causing a risk of leak currents.
It is known in electrical connection boxes to provide a stack of insulation plates carrying bus bars. Japanese Laid-Open Patent Application No. 2000-059951 shows a stack in which insulation boards and bus bars are vertical.
It is an object of the present invention to minimize risk that drops of water penetrating into an electrical connection box generate leak currents between the high-voltage bus bars, in the case where the electrical connection box mounted on a vehicle body is provided with a circuit to which a high voltage is applied.
According to the present invention, there is provided an electrical connection box for a vehicle adapted to be mounted in an engine compartment of the vehicle and to be connected to a voltage source of the vehicle having a nominal maximum voltage of not less than about 14V and not more than about 200V. The electrical connection box has a casing having a rear wall which in use is mounted against an upstanding wall of the vehicle, a front wall spaced from the rear wall, a pair of side walls extending between the front and rear walls and a bottom wall sloping downwardly in the direction from the front wall to the rear wall, the bottom wall having at least one water drainage hole at its lowermost portion adjacent the rear wall, and a plurality of electrical circuit insulation plates mounted in the casing having main faces parallel to the rear wall, and a plurality of bus bars mounted on the main faces. The casing has electrical relay receiving elements, electrical fuse receiving elements and electrical connector receiving elements located on at least one of its front and side walls.
In a second aspect, the invention provides a vehicle having an engine compartment having an upstanding wall surface, a voltage source having a nominal maximum output voltage of not less than 14V and not more than 200V, and an electrical connection box mounted in the engine compartment. The electrical connection box has a casing having a rear wall located on the upstanding wall surface of the engine compartment, a front wall spaced from the rear wall, a pair of side walls extending between the front and rear walls and a bottom wall sloping downwardly in the direction from the front wall to the rear wall, the bottom wall having at least one water drainage hole at its lowermost portion adjacent the rear wall, and a plurality of electrical circuit insulation plates mounted in the casing having main faces parallel to the rear wall, and a plurality of bus bars mounted on the main faces. The casing has electrical relay receiving elements, electrical fuse receiving elements and electrical connector receiving elements located on at least one of its front and side walls. Electrical relays are mounted on the electrical relay receiving elements, electrical fuses are mounted on the electrical fuse receiving elements, and electrical connectors are mounted on the electrical connector receiving elements. At least one, preferably a plurality, of the bus bars are electrically connected to the voltage source.
The upstanding wall surface of the vehicle on which the rear wall of the electrical connection box is mounted is most preferably vertical, but may be inclined at not more than 45xc2x0, more preferably not more than 30xc2x0 to the vertical. Most preferably, therefore, the bus bars in the box are vertical.
The voltage applied to the bus bars is indicated as not less than 14V. In practice, for reasons given above, the high voltage in a vehicle, such as an automobile, to which the invention is applied, is more than about 14V, i.e. is about 28V or more, particularly about 42V or more.
As described above, because the bus bars are disposed upright, water which has penetrated into the gaps between the bus bars can be drained away easily. Thus it is possible to prevent a leak current from being generated between the bus bars. Further because relays, fuses and connectors are mounted on the vertical outer wall surfaces of the electrical connection box, open faces of cavities or sockets accommodating them extend vertically. Thus it is possible to prevent drops of water from penetrating into the electrical connection box via gaps at such cavities.
The bottom wall of the electrical connection box is inclined downwardly toward the surface of the vehicle body on which the electrical connection box is installed, and the drainage hole is formed at the lowermost position of the bottom wall. Thus drops of water that penetrate into the electrical connection box are discharged from the drainage hole. Discharged drops of water run by gravity along the vehicle body. Therefore, it is possible to prevent the drops of water from splashing on other component parts in the vehicle body.
Furthermore, when the electrical connection box is in contact with the vehicle body, heat generated by the high voltage is released by transmitting the heat to the vehicle body.
It is preferable that the high voltage to be applied to the high-voltage bus bar is about 42V. In this case, it is easy to provide the voltage applied to the high-voltage bus bar at about 42V by connecting in series three batteries each having a rated voltage of 12V (nominal maximum voltage: 14V) generally used in automobiles. Needless to say, it is possible to use a single battery having a maximum voltage of about 42V. The reason why the high voltage to be applied to the high-voltage bus bar is set to 42V is partly because using a voltage close to or above 50V for the high-voltage bus bar may be dangerous. The present inventors have conducted salt water experiments in order to ascertain the degree of risk when applying a voltage of 42V in an electrical junction box suitable for use in an automobile engine compartment. The experiments were done as follows:
1 ml of salt water was injected into each terminal hole of the casing of a junction box which had bus bars disposed inside. Electrical components such as relay, fuse, connectors, etc. were mounted on the casing. A voltage of 42V was applied to bus bars of the junction box for 8 hours and then suspended for 16 hours. This was repeated twice. There was initially no change to the bus bars and electrical components. After the third repetition, it was found that extra electric current passed between the bus bars generating heat, and a portion of bus bars was melted. The heat also melted resin around bus bars such as an insulation plate, casing and resin portion of electrical components adjacent the casing.
Accordingly, since damage did not occur until after the third exposure to salt water, it was confirmed that in consideration of conditions under normal use of an automobile, the application of the electric power at 42V to the electric/electronic component parts should not cause a problem.